class Solution {
public:
    int numDecodings(string s) {
        int n=s.size();
        vector<int> dp(n+1);
        dp[0]=1;
        dp[1]=s[1-1]!='0';
        

        for(int i=2;i<=n;i++)
        {
            if(s[i-1]!='0')dp[i]+=dp[i-1];
            int t=(s[i-2]-'0')*10+s[i-1]-'0';
            if(t>=10 && t<=26)dp[i]+=dp[i-2];
        }
        return dp[n];
    }
};
